In recent years, a technology called an environmental power generation (also referred to as an energy harvesting) that harvests an unused energy such as, for example, light energy or thermal energy that exists in an environment around us and converts the harvested energy into electric power is attracting attention.
In order to secure an operating voltage of a load, a plurality of power generation elements, such as solar cells or thermoelectric power generation elements outputting a DC voltage, are connected in series. However, when a power generation amount of each of the plurality of power generation elements is increased, a DC voltage to be supplied to a load may exceed the withstand voltage of a load (an upper limit of operating voltage of a load). For example, in a case of the solar cell, when the illuminance of incident light becomes higher, the DC voltage to be supplied to the load may exceed the withstand voltage of the load.
Conventionally, a circuit in which excess power is consumed by a transistor or a technology of separating some of a plurality of solar cell panels from a load is suggested when the power generated by the solar cells exceeds power demanded by a load.
Related technologies are disclosed in, for example, Japanese Laid-Open Utility Model Publication No. 62-158844, Japanese Laid-Open Patent Publication No. 2012-044070, and Japanese Laid-Open Patent Publication No. 2014-011386.